1. Field of the Invention
The present invention generally relates to a disc recording/reproducing system, and more particularly, to a disc recording/reproducing system for formatting of a disc according to the MCAV (Modified Constant Angular Velocity) system or the MCLV (Modified Constant Linear Velocity) system.
2. Description of the Related Art
The CAV (Constant Angular Velocity) system has been largely used for formatting a writable optical disc because it provides easy rotating system control, etc. However, recording/reproducing of voluminous image data has been necessary in recent years, and the MCAV system, which has a larger capacity, has been increasingly adopted.
In the MCAV system, as illustrated in FIG. 1, the recording capacity of the entire disc is increased by dividing the recording surface of a disc 600 into several zones concentrically and providing a greater number of sectors per track at the outer zones of the disc than the inner zones. In FIG. 1, numeral 601 designates the n-th recording zone from the inside of the disc 600, and numeral 602 designates the (n+1)-th recording zone that is one zone outside the n-th recording zone.
As the disc rotation is regulated to be constant as in the CAV system, the control of the rotating system is easy. However, there is a problem in that the data processor becomes complicated as a recording/reproduced data rate differs for every zone on the disc.
The complication of a circuit at the recording side is not a serious problem, but the processing at the reproducing side becomes complicated, as it might become necessary to adjust the reproduced signal waveform equalization in consonance with data rate changes and a change-over of a frequency in a data extracting PLL. Furthermore, there is a problem in that a high level of high-frequency processing technology is necessary at the outer zones as the recording/reproduced data rate becomes high at the outer recording zones.
As a method for solving these problems, there is known a disc recording/reproducing system adopting the MCLV system. In this system, the format of a disc medium is the same as the CLV system, but the revolution speed for each zone is variable and the recording/reproduced data rate is kept constant. In order to change the disc revolution speed, the rotating control becomes somewhat complicated, but as the disc revolution speed has been fixed for each zone, the control of the rotating system is relatively easy as compared with the CLV system, which requires controlling the rotation system while extracting at a data rate.
Recently, a writable optical disc is available to store program data and graphics data used by computers, etc. Therefore, it is important for such a disc to be able to record/reproduce data at high speed with high reliability.
However, pursuant to the advance of image/audio compression technology in recent years, a required data storage capacity has been reduced, and it has become possible to realize a digital video disc that is capable of recording/reproducing motion pictures and audio data as digital data on an optical disc.
When considering such uses as described above, not only is high speed recording/reproduction required but also a real time property for constant recording/reproduction of required data is important.
The MCLV system has merits as a system in which the data processing and rotating system control are relatively easy so that it is possible to achieve a large storage capacity. However, the MCLV system has a problem when used to record/reproduce motion picture data, etc. That is, there is no problem in recording/reproduction within one zone, but when recording/reproducing data continuously extending over multiple zones, there is a problem in that a data rate abruptly changes because a disc rotation cannot be changed quickly in correspondence with transitions between record zones.
FIG. 2 is a time chart showing a relationship between the disc revolution speed and data rates in the MCLV system. The disc revolution speed represented by waveform 700 cannot drop quickly, but it drops gently when the tracking operation of zones moves from the n-th record zone 601 to the (n+1)-th record zone 602. On the other hand, a reproduced data rate 701 becomes high temporarily when the tracking of record zones moves from the n-th record zone to the (n+1)-th record zone. Therefore, the data extracting PLL at the reproducing side cannot follow the quick change of the data rate. Also, the reproduction processing cannot be performed until the data rate frequency enters into the PLL pull-in range. So, there is a problem in that the reproduction processing is suspended until the disc rotation is stabilized. As a result, data cannot be reproduced constantly.
There is a method to compensate data that are omitted during the suspension period by storing reproduced data proportional to the suspension of the processing in a buffer memory in advance before a tracking operation moves to another record zone. However, this method requires a memory having a voluminous capacity for storing data for several tracks as it becomes necessary to make a retracing to the first sector of a zone after the disc rotation is stabilized. Furthermore, the complicated recording/reproduction processing is inevitable.
As described above, in the conventional MCLV system, there is a problem in that a sufficient measure could not be taken for a real time property required for realizing digital video disc, etc., in the data processing when the tracking of record zones moves from zone to zone.
As described above, according to the conventional MCLV system, there is a problem in that when data are continuously recorded/reproduced extending over the data record zones, a data rate changes abruptly and the data extracting PLL cannot follow the abrupt change of data rates and the reproduction processing has to be suspended temporarily until the disc rotation is stabilized and thus, the real time property is impaired.